In recent years, there is an increasing demand for liquid crystal displays, along with the development of personal computers, particularly the development of portable personal computers. The penetration rate of home liquid crystal displays has also increased, so that the market for liquid crystal displays is also in an expanding state. Recently, organic light-emitting display devices such as an organic EL display, which is a self-emitting display that provides high visibility, have also attracted attention as a next-generation image display device. These image display devices are required to show higher performances including higher image quality, such as better contrast and color reproducibility, and lower power consumption.
Color filters are used in these liquid crystal display devices and organic light-emitting display devices. For example, in liquid crystal display devices, light which passed through a color filter is colored in the colors of the pixels that constitute the color filter, and the colored lights are synthesized to form a color image. In organic light-emitting display devices, a color image is formed in the same manner as that of liquid crystal display devices, in the case where an organic light-emitting device, which emits white light, is used in combination with a color filter.
Under the circumstances described above, higher luminance, higher contrast and an improvement in color reproducibility are also required of color filters, increasingly.
In general, a resin composition for forming a color filter is used to form color layers of color filters, the composition comprising a pigment or dye as the color material. Compared to dies, pigments have better resistance properties, such as high heat resistance. However, sometimes color filters produced with pigments have insufficient luminance.
On the other hand, when dyes are used as the color material, color filters with high luminance can be obtained. However, the color filters have a problem with the resistance properties and contrast.
As a method of increasing the resistance properties of dyes, a method of forming a salt-forming compound has been known (for example, see Patent Literatures 1 to 3).
An example is disclosed in Patent Literature 1, in which a chloride ion or an aryl sulfate ion is used as a counter anion of a triarylmethane dye to improve heat durability of the triarylmethane dye.
In Patent Literature 2, as a method of obtaining a coloring resin composition which has not only excellent light resistance but also excellent heat resistance, a salt forming method has been reported, in which a salt is formed by using a sulfonated compound of a dye skeleton such as phthalocyanine or anthraquinone, which is the counter anion, in combination with a triarylmethane skeleton, which is the cation.
However, the salt-forming compounds described in Patent Literatures 1 and 2 are those which are basically dissolved in solvents for use. In Patent Literatures 1 and 2, therefore, no attention was paid to solvent resistance, and color filters obtained from the color resin compositions for color filters disclosed in Patent Literatures 1 and 2 showed insufficient solvent resistance, electric reliability and contrast.
In Patent Literature 3, as a method of obtaining a color composition for color filters with excellent color characteristics, heat resistance, light resistance and solvent resistance, a salt-forming compound comprising a triarylmethane basic dye and a sulfonated organic compound having at least two sulfonic groups, is disclosed. However, as will be shown below with comparative examples, the solvent resistance, electric reliability and contrast of the color filter obtained from the color composition of Patent Literature 3 were insufficient.
A polysiloxane dye is disclosed in Patent Literature 4, which is highly cross-linked by polysiloxane containing at least ten Si atoms. Due to its synthesis method, the polysiloxane dye disclosed in Patent Literature 4 is a mixture in which an unreacted compound having only one dye skeleton or dyes with different polymerization degrees are present. It is difficult to separate only a dye with a specific polymerization degree from the polysiloxane dye, so that there is a problem with the productivity of the polysiloxane dye. Since the polysiloxane dye contains a silanol group or alkoxysilyl group, a siloxane bond is formed between the polysiloxane dye(s) or between the polysiloxane dye and other component having a silanol group or alkoxysilyl group. As a result, there is a deterioration in the state of a solution or dispersion liquid comprising the polysiloxane dye, such as a change in solubility or an influence on dispersion stability, making it difficult to handle the solution or dispersion liquid. This reaction is likely to proceed especially by heating, so that the dye of Patent Literature 4 is not suitable for color filter applications. As will be shown below with comparative examples, the color filter comprising the polysiloxane dye had insufficient solvent resistance, electric reliability and contrast.